Service Code Help and other suggestions?

[crackpuppy]

Been searching this forum for code 55C4 and 54C6. Can't find anything about 55C4 but 55c6 has to do with transfer case fluid. Does anyone know what 55C4 relates to? I have a 2004 BMW X5 3.0i and started to receive the DSC 4X4 inactive light. I'm going to attack this by getting an alignment and replacing the transfer case fluid. You guys think I should replace alternator and/or transfer case actuator? I've been getting a lot of vibration when idled at a red light, my mechanic believes all 4 motor mounts needs to be changed. He says he needs about 6 hours of labor. Does this sound about right? Thank you for reading. Your Replies are much appreciated.